The human growth hormone (hGH) gene cluster encompasses both pituitary- and placenta-specific genes that are essential for normal growth and development. A set of tissue-specific, dominantly acting distal regulatory elements, the locus control region (LCR), were mapped between 14 and 34kb 5' to the cluster on the basis of DNaseI hypersensitivity (HS) in chromatin derived from expressing tissues. These elements are involved in appropriate activation of hGH gene cluster expression in pituitary/placenta. However the specific functional role of each HS, the level of redundancy among these determinants, and their respective mechanism(s) of action are not defined. The organization of genes in the hGH gene cluster, their high-level expression and mutually exclusive tissue-specificities, and the corresponding specific sets of LCR elements make it a valuable model for studying gene expression. Aim I is to functionally analyze the subset of LCR HS restricted to either pituitary (HSI,II) or placenta (HSIV). These elements will be studied in the context of a large (P1) human transgene (hGH-P1). This 87kb hGH-P1 transgene encompasses the entire set of LCR elements (HSI-V) and most of the contiguous hGH gene cluster and the genes are expressed in appropriate tissues in the host mouse. A small, well-characterized functional segment of the HSI,II will be deleted from hGH-P1 and its impact on hGH gene cluster expression will be investigated in the transgenic mouse. In parallel the same approach will be applied to the placental-specific, HSIV to delineate its function in activating and/or restricting placental expression. The mechanism(s) of HS function will be studied in each case by characterizing the effects of these deletions on chromatin epigenetic modifications relative to the native hGH-P1. Aim II will identify and characterize corresponding LCR control elements in the mouse (m). A major goal of this aim will be to determine whether an LCR also directs mGH gene expression. Specifically we will identify the presence of HS and their sequences will be compared to the corresponding human elements. These data will be used to establish phylogenetic footprints of critical HSI,II determinants and serve as the foundation for the ongoing functional/mechanistic analyses in Aim I, including the generation of mice with corresponding targeted deletions. Significance: These studies will provide novel insight into the role(s) played by the LCR elements in the establishment and maintenance of appropriate gene expression profiles during development and in disease-related expression patterns of the hGH gene.